The proposed project combines non-destructive optical measurements with electronmicroscopy and conventional biochemical analysis to investigate the sequences of reactions involved in the production of hydrochloric acid by the gastric mucosa. Specific aspects of the proposal include studies of the morphologic changes associated with the onset and cessation of acid secretion; the in situ measurement of cytochrome redox states as a measure of metabolic activity; continuous monitoring of intracellular pH as an index of secretory state; and, measurements of cyclic AMP for determination of the role of this compound in stimulus-secretion coupling. The goal of the project is to inter-relate the various measurements in order to obtain a rather complete picture of the events which occur between the addition of a stimulating agent and the final production of acid.